Separation of aromatic hydrocarbons from aliphatic hydrocarbons using ketodioxane



Oct. 27, 1959 B. B. LAMPERT ETAL 2,910,518

SEPARATION OF AROMATIC HYDROCARBQNS FROM ALIPHATIC HYDROCARBONS USINGKETODIOXANE Filed June 25, 195": 3 Sheets-Sheet 3 Me'fhylnaph'lhalenesA?! AVA )XIAA ll 02 -0 Y AvAv 6 Am Kefodioxane BERNARD B LAMP Decalin JAsv. RRAY,

DAV W.P K

United States Patent SEPARATION OF AROMATIC HYDROCARBONS FROM ALIPHATICHYDROCARBONS USING KETODIOXANE Bernard B. Lampert, Pittsburgh, Pa., andJames V. Murray, Jr., and David W. Peck, South Charleston, W. Va.,assignors to Union Carbide Corporation, a corporation of New YorkApplication June 25, 1957, Serial No. 667,878

5 Claims. (Cl. 260-674) This invention relates to chemical processes.More particularly, it relates to the separation of aromatic hydrocarbonsfrom admixture with aliphatic hydrocarbons using ketodioxane.

In the common raw material sources of hydrocarbons for the chemicalindustry there are usually found intimate mixtures of aromatic andaliphatic hydrocarbons. This is true whether the hydrocarbons arederived from petroleum sources such as oil or shale, or fromcarbonaceous materials such as coal tar fractions or coal hydrogenationproduct fractions. Such mixtures, regardless of source, must ordinarilybe separated into generally aromatic and non-aromatic fractions as aprerequisite to their commercial utilization. Our invention has beendeveloped using coal hydrogenation fractions (as well as artificialbinary mixtures) and is described and illustrated below with such coalhydrogenation products. However, it is in no sense limited to thesematerials but is generally applicable to any mixture of aromatic andaliphatic hydrocarbons regardless of source.

Due to the prevalence of such mixtures and the demand for theirseparated components, numerous methods have been suggested for theseparation of aromatic compounds from aliphatic compounds. Prominentamong the methods suggested have been those involving extraction with aselective solvent, usually extraction of the aromatic compounds by thesolvent. Solvents suggested for this purpose have included suchcompounds as liquid sulfur dioxide, which requires speciallowtemperature equipment, and ethylene carbonate, which is difficult torecover without decomposition, as well as others such as ethylene glycolwhich is somewhat limited in the range of compounds it can separate. i

We have now discovered that ketodioxane is useful as a selective solventfor separating aromatic hydrocarbons from aliphatic hydrocarbons. It isparticularly desirable as a solvent when applied to a broad and complexaromatic-aliphatic mixture such as coal hydrogenation neutral light oil,a gross aromatic-nonaromatic oil fraction having a boiling temperaturerange of 100 C. to 260 C. and from which most of the acidic and basicconstituents have been removed. Ketodioxane can also be called (2-hydroxyethoxy) acetic acid laotone and can be represented by theformula: r

Hg CH:

(It is potentially an inexpensive, easily available solvent, beingreadily produced in good yield by the catalytic dehydrogenation ofdiethylene glycol.

I In the drawings:

Figure 1 is a schematic representation of an embodiment of the inventionwherein the aromatic hydrocarbons are separated from the ketodioxaneextract by distillation.

Figure 2 is a schematic representation of an embodi- 2,910,518 PatentedOct. 27, 1959 ment of the invention wherein the aromatic hydrocarbonsare separated from the ketodioxane extract by back extraction with analiphatic naptha.

Figure 3 is a schematic representation of an embodiment of the inventionwherein the aromatic hydrocarbons are separated from the ketodioxaneextract by hydrolyzing the ketodioxane and removing it in water.

Figure 4 is a ternary diagram of the relative solubilities of benzene,normal heptane and ketodioxane.

Figure 5 is a ternary diagram of the relative solubilities ofmethyl-naphthalenes (50% alphaand 50% beta-), decalin and ketodioxane.

Figure 6 is a ternary diagram of the relative solubilities of tetralin,decalin and ketodioxane.

In the practice of the invention, the aromatic-aliphatics mixture,whether a simple binary mixture of two compounds or a complex mixturesuch as coal hydrogenation neutral light oil, is contacted withketodioxane which preferentially dissolves or extracts the aromatichydrocarbons. The ketodioxane extract of aromatics is removed from thealiphatics and the aromatics are recovered from the extract. Theextraction of the aromatics with ketodioxane must be conducted at atemperature above 28 C., which is the freezing point of ketodioxane.Temperatures between 30 C. and 60 C. will be found suitable for mostapplications, although higher temperatures may be employed if desired.However, the temperature of the extraction should not approach theboiling point of the lowest boiling component of the mixture beingextracted. Atmospheric pressure is suitable for the extraction and ispreferred. If desired, however, subatmospheric or superatmosphericpressure could be employed. In varying the temperature and/ or thepressure, the most important consideration is that these conditionsshould be such that the aromaticraliphatics: feed mixture, theketodioxane solvent, the extract and the ratfinate will all remain thethe liquid state during the actual extraction.

For the most effective separation of the aromatic hydrocarbons from thealiphatics, a multistage extraction apparatus is preferred. The relativequantity of ketodioxane employed as solvent is not extremely criticaland may vary from as little as one part by weight of ketodioxane for 20parts by weight of aromatic-aliphatic mixture to as much as 20 parts byweight or more of ketodioxane for one part by weight of mixture. Therelative quantity used will of course be influenced by the proportion ofaliphatics in the mixture. We have found that for neutral light oilmixtures from coal hydrogenation between 2 and 3 parts by weight ofketodioxane to one part by weight of neutral light oil is preferred.

When the extraction has been accomplished the aliphatic hydrocarbons areleft as product and the aromatic hydrocarbons are in the ketodioxaneextract and must be recovered therefrom. The boiiing point ofketodioxane is 216 C. If the aromatics which have been extracted by theketodioxane all boil at temperatures appreciably below 216 C. they maybe readily separated from the ketodioxane by distillation according tothe embodiment of the invention illustrated in Figure 1 of the drawing.Such distillation is normally at atmospheric pressure althoughsubatmospheric or superatmospheric pressures could be used if desired.This embodiment is most useful in separating simple mixtures ofaromatics and aliphatics when there is only one or a few aromatichydrocarbons all boiling below 216 C. When any of the aromatics beingseparated have boiling points close to that of ketodioxane, distillationis not available for the separation and other means must be employed.

One such means involves back extraction with a naphtha and isillustrated in Figure 2 of the drawing. In this embodiment of theinvention the ketodioxane extract of aromatic hydrocarbons is itselfextracted, that is, back extracted, with an aliphatic naphtha. Thealiphatic naphtha, being miscible with aromatic hydrocarbons butimmiscible with the ketodioxane, extracts the aromatic hydrocarbons andleaves the ketodioxane for reuse. The aliphatic naphtha is chosen tohave a boiling point temperature substantially different from theboiling pointtemperatures of any of the aromatic hydrocarbons so that itmay be readily separated from them by distillation. Aliphatic naphthasuseful in the invention include pentane, hexane, heptane and octane, andany of their isomers, as well as cyclopentane, methylcyclopentane,dimethylcyclopentane, ethylcyclopentane, cyclohexane, andmethylcyclohexane, as well as petroleum ether fractionshaving boilingtemperatures below 120 C.

Like the principal ketodioxane extraction thenaphtha back extractionmust be conducted at a temperature above 28 C. and below the boilingpoint temperature of any of the compounds. emperatures between 30 C. and60" C. havebeen found generally suitable. Atmospheric pressure issuitable for the back extraction and is preferred. If desired, however,subatmosphericor superatmospheric pressure could be employed. In varyingthe temperature and/ or the pressure, the most important considerationis that these conditions should be such that the ketodioxane-aromaticsfeed solution, the aliphatic naphtha solvent, the extract and theraffinate will all remain in the liquid state during the backextraction.

'For tl e most ehfective back extraction of the aromatics from theketodioxane a multistage extraction ap paratus is preferred. Therelative quantity of aliphatic naphtha employed as back extractant isnot extremely critical and may vary from as little as'one part by weightof naphtha for 20 parts by weight of ketodioxane-aromatics solution toas much as 20 parts by weight or'more of naphtha for one part by weightof ketodioxane-aromatics solution. The relative quantity used will ofcourse be influenced by the proportion of aromatics to ketodioxane inthe solution. We have found in work with neutral light oil mixtures fromcoal hydrogenation that between 0.5 and 4 parts by weight of aliphaticnaphtha per one part by weight of ketodioxane-aromatics.solution ispreferred. When the back extraction has been accomplished the naphthacan be distilled from the naphthaaromatics solution and the aromaticsdistillant can then be Water washed, if desired, to remove residualketodioxane.

Another method of separating the aromatics from the ketodioxane extractthereof, which can be employed when any of the aromatics being separatedhave boiling points close to that of ketodioxane, is illustrated inFigure 3 of the drawing. In this embodiment of the invention water isadded to the ketodioxane extract of aromatics. Addition of the watercauses the ketodioxane to hydrolyze to (Z-hydroxyethoxy) acetic acidwhich dissolves in the water. The mixtures separates into an aromaticslayer and a water layer with the (Z-hydroxyethoxy) acetic acid dissolvedin the water layer. The layers are then removed separately. The additionof the water, hydrolysis and separation of the layers are normallyconducted at room temperatures and atmospheric pressure, althoughelevated temperature and subatmospheric or superatmospheric pressurecould be employed provided all components remained in the liquid state.After separation of the layers, the water solution of (.2-hydroxyethoxy)acetic acid is distilled at atmospheric pressure and after the water,including the water of hydrolysis, is removed: as distillate, theketodioxane is recovered as. distillate for reuse. The aromatic layercan be washed with water if desired, to remove any traces ofketodioxane.

The embodiments of the invention can be described in detail withreference to the drawings.

In Figure 1 of the drawing is illustrated the embodiment of theinvention wherein a hydrocarbon mixture is extracted with ketodioxane inthe extractor 11 and the ketodioxane is recovered from the extract instill 16. This embodiment is used when the aromatic hydrocarbon beingseparated will not co-distill with ketodioxane.

The hydrocarbon mixture is introduced into the extractor 11 through line12. Concurrently ketodioxane is introduced into the extractor 11 throughline 13. As the extraction proceeds the ketodioxane extract of arcmatichydrocarbon is removed from the extractor 11 through line 14. Therafiinate from the extraction is the nonaromatic hydrocarbons which areremoved from the extractor 11 through line 15 as product. Theketodioxane-aromatics extract removed through. line 14 is conductedtherein into a still 16. As distillation proceeds the ketodioxane andthe aromatic hydrocarbons are removed as distillate, the lower boilingof the two being distilled off first. The aromatics are removed asproduct through line 17. The ketodioxane is removed through line 18 andrecycled therein to the ketodioxane feed line 13, for reuse in theextractor 11.

Figure 2; of the drawing illustrates a second embodiment of theinvention wherein the hydrocarbon mixture is extracted with ketodioxanein extractor 21' after which the ketodioxane-aromatics extract isback-extracted with an aliphatic naphtha in a second extractor 22', fromwhich the ketodioxane is recycled for reuse. The naphtha-aromaticsextract is distilled in still 23 to remove the naphtha for recycle. Thearomatic hydrocarbons are then water washed in a third extractor. 2.41and removed therefrom as product. This embodiment may be employed wherethe aromatichydrocarbons and ketodioxane have boiling points closetogether or azeotrope, so as to co-distill.

The hydrocarbon mixture is introduced intothe first extractor 21 throughline 25. Concurrently ketodioxane.

is introduced into the extractor 21 through line 26., Asthe extractionproceeds the ketodioxane extract of 'aro,. matic hydrocarbons is removedfrom extractor 21 through line 27. The raffinate from the extraction isthe non aromatic hydrocarbons which are removed from; the extractor 21through line 28 as product. The ketodioxanearomatics extract removedthrough line 27 is conducted therein into a second extractor 22 whereinit is backextracted. with an aliphatic naphtha which is introduced intothe, extractor 22 through line 29. As the backextraction proceeds thenaphtha extract of aromatics is removed from the extractor 22 throughline 30. The; ketodioxane residue from the back-extraction is removedfrom the extractor 22 through line 31 and recycled therein to theketodioxane feed line 26 for reuse in the process.

The naphtha extract of aromatics removed through line 30 is conductedtherein into the still 23. As the; distillation proceeds in still 23 thenaphtha distillate; is

removed from the still 23 through line 32 and recycled therein to thenaphtha feed line 29 for reuse in the process. the still 23 through line33 and conducted therein into extractor 24. through line 34: Inextractor 24 the water washes, any

residual traces of ketodioxane out of the aromatics and ketodioxaneoccurs in a water layer which separates-.

from the aromatics. The aromatics are then conducted: to an extractor 43where they are washed with water and then recovered therefrom asproduct. The water solutionof (Z-hydroxyethoxy) acetic acid, thehydrolysis productof ketodioxane, isconducted to a still 44 where Thedistillate of aromatics is removed from Water is introduced intoextractor 2,4.-

extractor '43.

arrears the Water is first removed' as distillate and "the ketodioxaneis then recovered as distillate .for recycleand reuse.

The hydrocarbon mixture is introduced into the "first extractor 41through line 45. Concurrently ketodioxane -issintroduced into theextractor 41 through line 46. As the extraction proceeds the ketodioxaneextract of aroma'tic hydrocarbons is'renioved from extractor 41 throughline 47. The :rafiinatefrom .the extraction is the nonaromatichydrocarbons which are removed from the ex -tractor 41 through line48aslproduct. The ketodioxanearomatics extract removedthrough line 47 isconducted therein into a mixing-settling tank 42. Water is introducedinto the tank 42 through line 49 and as it mixes with 'theketodioxane-aromatics extract the ketodioxane is =converted byhydrolysis to (2-hydroxyethoxy) acetic acid and dissolved in the water.Upon standing the aro matic-hydrocarbons rise to the surface andseparate from the water solution so that two layers are formed. Thewater'solutionof (Z-hydroxyethoxy) acetic acid is with- "drawn :from thetank42 through line 50.

The aromatic hydrocarbons are removed from the tank 42 through line 51wherein they are conducted into an Water is introduced into extractor 43throughline-SZ. In extractor 43 the water washes any "residual :tracesof ketodioxane out of the aromatics and the washed aromatichydrocarbonsare removed from the extractor-43 as :product through line 53. The washwater with traces'of ketodioxane is removed from the extractor -43through li-ne54. The water solution of (2-hydroxyethoxy) acetic acid -inline 50 is conducted therein into a still 44. :As distillation proceedsin still 44 the (2- hydroxyethoxy) acetic acid is converted back toketodioxane as the water, including the water of hydrolysis, is removedfrom the still 44 first as distillate through line 55. The ketodioxaneis then'removed from the still 44 as distillate through line 56andrecycled therein to the ketodioxane feed line 46 for reuse in theprocess.

The eifica'cy of the separations obtained in the examples below 'are'deinonstr'ate'dby reference to mixed aniline point andtorefractive-index. The mixed aniline point in each case was determinedaccording to ASTM method;D-10125 1. The method consists of mixingtogether one part by volume of the sample being tested, one part byvolume'of-normal-heptane and two parts by volume of aniline, :and thenobserving 'the temperature at which the mixture changes vfrom onehomogenous solution to two liquid phases, this temperature being theso-called mixed aniline poin The mixed aniline point is consideredindicative of aromaticity, inasmuch as aromatic hydrocarbons haverelatively lower mixed aniline points, and nonaromatic hydrocarbons haverelatively higher mixed aniline points. For example, the mixed anilinepoint of normal-heptane is 69 C., of methylcyclohexane is 54 C., oftransdecalin is 50 C., of 1- methylnaphthalene is 13 C., of toluene isC. and of tetralin is 9 C.

The refractive index is also considered indicative of aromaticity, withthe more aromatic hydrocarbons having relatively higher refractiveindexes. The refractive index, n of normal-heptane is 1.3875, ofmethylcyclohexane is 1.4225, of toluene is 1.4950, of trans-decalin is1.4700, of tetralin is 1.5461, and of l-methylnaphthalene is 1.6180.

Example I The hydrocarbon mixture separated was a neutral light oilderived from coal hydrogenation. It had a refractive index, 11 of 1.5120and a mixed aniline point of 323 C. It contained 26 percent by weight ofaliphatic hydrocarbons and 75 percent aromatic hydrocarbons.

The equipment comprised a l2-stage, 2 inch inside diameter York-Scheibelextraction column. The temperature of the materials during theextraction process was fmaintain'ed rat 50 C. The feed to the extractioncolumn was 2 parts of volume -'of ketodioxane to one part 'by volume ofhydrocarbon mixture. The ketodioxane extract from the column was foundto contain '65 percentrby weight 'of the hydrocarbon mixture with theother 35 apercentby weight remaining as raffinate.

'When L1 800.milliliters ofwater was added to 2808 grams of the extractan aromatic hydrocarbon phase separated. After being washedwith waterthis aromatic hydrocarbon extract phase amounted to 550 grams. It :hada'refractive index of 1.5418 and a mixed aniline point of 18.4 C. Thisaromatic hydrocarbon extract .contain'ed'98 percent by weight o'faromatic hydrocarbons and only 'tWmperce'nt by weight of aliphatichydrocarbons. The water phase rofxthe extract was washed with hexane toremove residual hydrocarbons and then distilled. Ketodioxane in theamount of 1900 grams was recovered as distillate.

The raflinate remaining after :the extraction with ketodioxane :had -arefractive index of 1.4613 and amixed aniline .point of 515 .C. .Itconsisted. of '58 percent by weight of aliphatic hydrocarbons and 42percent aromatic. hydrocarbons.

Example 11 The hydrocarbon mixture separated consisted of 56 percent by-Wight=.0f benzene and 44 percent by weight of n-heptane. Theketodioxane employed as extractant had a freezing point of 24.8 C.

The equipment comprised a four foot long, 11 stage, 1 inch insidediameter York-Scheibel extraction column. The temperature of thematerials during the extraction process was :maintained at 40 C. Thefeed to -the extraction column was 2 parts by volume of ketodioxane to:1 part by volume of hydrocarbon mixture. Feed to the extraction columnwas commenced'and the column was allowed to come to equilibrium.Then'while 776 .grams (1000 milliliters) of the hydrocarbon mixture wasextracted with2534 grams (.2000 milliliters) of ketodioxane,.there wasobtained from the column 2927 grams ofextract and 306 grams ofrafiinate.

The extract was charged to a laboratory still having a 2 foot by 1 inchinside diameter column, and the extract was distilled ata reflux ratioof 3 to 1 until the distillationtemperature began to rise rapidly aboveC. The .distillate up to this point, being the material extracted by theketodioxane from the original hydrocarbon mixture, amounted to 448 gramsand contained 93 percent by Weight of benzene and only 7 percent byweight of heptane. The distillation was continued to recover theketodioxane and 2327 grams of ketodioxane, having a freezing point of26.5 C., was recovered.

The composition of the rafiinate from the extraction, on a solvent-freebasis, was 98 percent by weight of heptane and only 2 percent by weightof benzene.

Example III The hydrocarbon mixture separated was a neutral light oilderived from coal hydrogenation. That fraction of the mixture having aboiling temperature between C. and 260 C. was analyzed and found to havea refractive index, 21 of 1.5113 and a mixed aniline point of 328 C. Itcontained 26 percent by weight of aliphatic hydrocarbons and 74 percentof aromatic hydrocarbons.

The equipment comprised a four foot long 1l-stage, 1 inch insidediameter York-Scheibel extraction column. The temperature of thematerials during the extraction process was maintained at 50 C. The feedto the extraction column was 3 parts by volume by ketodioxane to 1 partby volume of hydrocarbon mixture. Feed to the extraction column wascommenced and the column was allowed to come to equlibrium. Then while901 grams (1 liter) of the hydrocarbon mixture was extracted with 3735grams (3 liters) of ketodioxane, there '7 was obtained from the column4228 grams of extract and 360 grams of rafiinate.

The extract was back-extracted, in the same type of column as that usedfor the original extraction, with n-heptane at a n-heptane to feed ratioof 2 to 1 so as to recover the aromatic hydrocarbons which had beenextracted by the ketodioxane. The n-heptane was distilled from then-heptane extract and the residue was washed with water, leaving 515grams of aromatic hydrocarbons. The fraction of the material boilingbetween 120 C. and 260 C. was analyzed and found to have a refractiveindex of 1.5452 and a mixed aniline point of l7.4 C. It contained 97percent by Weight of aromatic hydrocarbons and only 3 percent by weightof aliphatic hydrocarbons. The ketodioxane raifinate from the nheptaneback-extraction was found to have a freezing point of 25.5 C. and to besuitable recycle in the process.

The aliphatic hydrocarbon rafiinate from the. original ketodioxaneextraction was washed with water to remove any traces of ketodioxane.The fraction of it boiling between 120 C. and 260 C. was analyzed andfound to have a refractive index of 1.4605 and a mixed aniline point of53.2 C. It contained 61 percent by weight of aliphatic hydrocarbons.

Further examples of the eflicacy of ketodioxane as a selective solventfor extracting an aromatic compound from admixture with an aliphaticcompound are to be seen in the results plotted in Figures 4, 5 and 6 ofthe drawing. Each of these figures is a ternary diagram representing therelative miscibility of ketodioxane with an aliphatic and an aromaticcompound. The data for these figures was all gathered at a temperatureof about 25 C. These ternary diagrams clearly demonstrate to one skilledin the art the efiiciency of ketodioxane in the aforesaid extractiveseparation.

What is claimed is:

1. Process for separating a more aromatic hydrocarbon fraction fromadmixture with a less aromatic hydrocarbon fraction which comprisesextracting said more aromatic fraction with ketodioxane to leave saidless aromatic fraction as product and recovering said more aromaticfraction from the extract thus obtained.

2. Process for separating a more aromatic hydrocarbon fraction fromadmixture with a less aromatic hydrocarbon fractionwhich comprisesextracting said more aromatic fraction with ketodioxane to leave saidless aromatic fraction as product and distilling said more aromaticfraction from the extract thus obtained.

3. Process for separating a more aromatic hydrocarbon fraction fromadmixture with a less aromatic hydrocarbon fraction which comprisesextracting said more aromatic fraction with ketodioxane to leave saidless aromatic fraction as product, back-extracting the first extractthus obtained with an aliphatic naphtha to remove the more aromaticfraction as a second extract and distilling said naphtha from saidsecond extract to leave said more aromatic fraction as product.

4. Process for separating a more aromatic hydrocarbon fraction fromadmixture with a less aromatic hydrocarbon fraction which comprisesextracting said more aromatic fraction with ketodioxane to leave saidless aromatic fraction as product, diluting the first extract thusobtained with water and thereby hydrolyzing the ketodioxane to(Z-hydroxyethoxy) acetic acid, separating the thus formed aromatichydrocarbon phase from the thus formed water-acid phase and recoveringsaid aromatics as product.

5. Process for separating a more aromatic hydrocarbon fraction fromadmixture with a less aromatic hydrocarbon fraction which comprisesextracting said more aromatic fraction with ketodioxane to leave saidless aromatic fraction as product, diluting the first extract thusobtained with water and thereby hydrolyzing the ketodioxane to(Z-hydroxyethoxy) acetic acid, separating the thus formed aromatichydrocarbon phase from the thus formed water-acid phase, and distillingthe wateracid phase to recover ketodioxane as distillate and recoveringsaid aromatics as product.

References Cited in the file of this patent UNITED STATES PATENTS2,568,159 Medcalf et al. Sept. 18, 1951 2,568,176 Vriens et al. Sept.18, 1951 FOREIGN PATENTS 413,307 Great Britain July 11, 1934 472,767Great Britain Sept. 30, 1937 OTHER REFERENCES Ham: Ind. and Eng. Chem.,vol. 46, pp. 390-392, 1954. (Copy in Patent Ofiice Library.)

1. PROCESS FOR SEPARATING A MORE AROMATIC HYDROCARBON FRACTION FROMWHICH COMPRISES EXTRACTING SAID MORE CARBON FRACTION WHICH COMPRISESEXTRACTING SAID MORE AROMATIC FRACTION WITH KETODIOXANE TO LEAVE SAIDLESS AROMATIC FRACTION FRACTION AS PRODUCT AND RECOVERING SAID MOREAROMATIC FRACTION FROM THE EXTRACT THUS OBTAINED.